This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2016 New J. Chem., 2016, 40, 5577--5587 | 5577 Cite this: New J. Chem., 2016, 40, 5577 Polymorphic study and anti-inflammatory activity of a 3-cyano-2-pyridone based flexible model† Sunil K. Rai, Praveen Singh, Shaziya Khanam and Ashish K. Tewari* This work deals with the synthesis, crystallization and the polymorphic interpretation of 2-{3-[3-cyano-6- methyl-2-oxo-4-phenylpyridin-1(2H)-yl]propoxy}-4-methyl-6-phenylnicotinonitrile (2). The quantitative analysis of the two polymorphs has been achieved through single crystal X-ray diffraction and Hirshfeld surface analysis. However, differential scanning calorimetry has been performed to determine the thermal stability and density functional theory to interpret the conformation on the propylene linker. Furthermore, the binding affinity of compound 2 was evaluated through a docking study in the COX-2 active site. An in vivo study revealed significant anti-inflammatory activity. Moreover, solubility of both polymorphs was checked in a 50% MeOH–water mixture and phosphate buffer (pH = 7.40). 1. Introduction 2-Pyridone analogues have wide occurrence in natural products and medicines. 1–6 Recently, their flexible dimers have been reported as active anti-inflammatory agents. 7–9 Therefore, the design of 2-pyridone based flexible molecules has now attracted much attention, due to their resemblance with celecoxib and existence of a greater number of rotatable dihedral angles. Owing to a higher flexibility than celecoxib, these molecules deform their geometry on low cost expenditure of energy to make closer noncovalent interactions with the neighbouring side chain residues in the active site of the COX-2 enzyme. In medicinal chemistry, it is an important target to design such new drug candidates. Because of their ethnic feature, conformationally flexible molecules have a high tendency to form polymorphs due to a greater number of torsion angles accessible under ambient conditions compared to rigid molecules. 10–12 Furthermore in pharmaceuticals, poly- morphism plays a pivotal role to improve relevant properties, such as hygroscopicity, stability, solubility, dissolution rates and bioavailability. 13–15 Each form of a polymorph varies in their structural properties on grounds of variation in conformation and molecular packing in their solids. In these solids, crystal forces play a crucial role in determining the conformation and packing pattern in the crystal lattice. 16–20 Therefore, the study of inter and intramolecular noncovalent interactions (i.e., C–HÁÁÁN, C–HÁÁÁO, C–HÁÁÁp, and pÁÁÁp) in their crystal structures is important. 21–25 This report deals with the synthesis, crystallization, polymorphic studies, conformational analysis, docking and anti-inflammatory study of 2-{3-[3-cyano-6-methyl-2-oxo-4-phenylpyridin-1(2H)-yl]- propoxy}-4-methyl-6-phenylnicotinonitrile (2). The molecule 2 is a 2-pyridone based flexible model in which two pyridone units cap the two ends of a –(CH 2 ) 3 – linker. Crystallization of 2 after column chromatography in chloroform and ethyl acetate delivered two polymorphs (i.e. forms I, and II, respectively). Their intermolecular interactions in crystal packing have quantitatively been investigated through single crystal X-ray diffraction and Hirsfeld surface analysis; however, the conformational stability of polymorphs has been determined by density functional theory (DFT). Furthermore, a docking study has been performed to know the binding affinity of compound 2 in the COX-2 active site and the anti-inflammatory activity of compound 2 was evaluated by the complete Freund’s adjuvant (CFA)-induced rat paw edema method. 2. Experimental section 2.1 General methods All reactions were performed in ordinary conditions at ambient temperature and reagents were used without further purification. 1 H and 13 C NMR spectra were recorded on a JEOL AL300 FT-NMR Spectrometer (300 MHz for 1 H and 75 MHz for 13 C). TMS was used as an internal reference and chemical shift values are expressed in d ppm units. Differential scanning calorimetry (DSC) analysis was performed on a Mettler Toledo TC 15 TA under an N 2 purge from 30 to 250 1C at a heating rate of 5 1C min À1 . Fourier transform infrared (FT-IR) spectra of the synthesized compounds in a KBr pellet were recorded using a Varian 3100 FT-IR Excalibur spectrophotometer. Department of Chemistry (Center of Advanced Study), Institute of Science, Banaras Hindu University, Varanasi 221005, India. E-mail: tashish2002@yahoo.com † Electronic supplementary information (ESI) available. CCDC 949747 and 949921. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5nj03683f Received (in Montpellier, France) 24th December 2015, Accepted 15th April 2016 DOI: 10.1039/c5nj03683f www.rsc.org/njc NJC PAPER